Effect of pressure on phonon modes in wurtzite zinc oxide

The pressure dependence of first- and second-order Raman frequencies of wurtzite ZnO has been measured up to the wurtzite-rocksalt phase transition pressure of 8.3 GPa, A small increase of the LO-TO splitting with increasing pressure is observed. This effect is related to the combined pressure dependences of the electronic dielectric constant in the phonon region and Born's transverse dynamic effective charge. Our results indicate a rather weak dependence of the dynamic charge on pressure, a behavior which is similar to that found for GaN, AlN, and SiC and different from that of other polar tetrahedral semiconductors.